Simon Lewis is having some trouble adjusting to his new life as a vampire, especially now that he hardly sees his best friend Clary, who is caught up in training to be a Shadowhunter - and spending time with her new boyfriend, Jace. Simon decides he needs a break and heads out of the city - only to discover that sinister events are following him. Realizing that the war they thought they'd won might not yet be over, Simon has to call on his Shadowhunter friends to save the day - if they can put their own splintering relationships on hold long enough to rise to the challenge.